Group members:

 

Main areas of research

 

● Studying the effect of spin-polarized current on coercivity fields of tunneling magnetoresistance in pressed powder composites made of half-metal CrO2 nanoparticles.

 

● Studying electron transport properties in carbon nanotubes and graphite nanoplatelets through quantum corrections to resistance caused by the effects of weak localization and electron-electron interaction.

 

● Investigation of kinetic properties of a two-dimensional electron gas in perpendicular and parallel magnetic fields.

 

● Studying the effect of spontaneous violation of stoichiometric composition in Sr-substituted lanthanum cuprates at ultra-low degrees of alloying.

 

 

Equipment

 

● Equipment for in situ studies of galvanomagnetic properties of quench-condensed thin metal films in magnetic fields up to 6 T in the temperature range 0.3 – 300 K Deep oil-free vacuum is provided by zeolite pumps, a magnetic discharge diode pump, and a high-vacuum pump of the «Orbitron» type.

 

● Revolving at an arbitrary angle Kapitsa’s-design solenoid with a cryostat for studies of galvanomagnetic anisotropy of single crystals. Magnetic field sweeping from   0.03 to 2 T with a smooth transition through zero in the temperature range from 4.2 to 450 K.

 

● Equipment for studies of galvanomagnetic and thermomagnetic properties of metal and semiconductor specimens of single crystals and films in the temperature range from 1.6 to 350 K with a steady or sweeping smoothly from – 2 T to + 2 T magnetic field.

 

● Equipment with superconducting solenoid for quantum oscillations measurements (magnetic fields up to 6 T  in  the temperature range 1.7 – 300 K). Simple compensation method and high selective deep modulation of magnetic field method are provided.

 

● Equipment for studying  single crystal samples conductivity and quantum oscillations under uniaxial compression (magnetic field up to 6 T in the temperature range 1.7 – 4.2 K).

 

● Equipment for studies of galvanomagnetic properties of samples in pulse magnetic field of 16 ms up to 20 T.

 

 

Important results in recent years

 

● Highly oriented pyrolytic graphite was used to obtain the cobalt intercalated graphite compound in a two-step synthesis method. Resistance, magnetoresistance, and Hall coefficient were experimentally studied in the temperature range of (1.6÷293) K and magnetic field up to 5 T. The measurements show that asymmetric and linear relatively to magnetic field magnetoresistance is not saturated with an increasing magnetic field up to 5 T and is not dependent on temperature. The effect of linear magnetoresistance can be explained within Abrikosov's model of quantum magnetoresistance [1].

 

● Quantum effects in p-type Si0.2Ge0.8/Ge/Si0.2Ge0.8 heterostructure with extremely high mobility of charge carriers μH = 1367000 cm2/(V⋅s) have been comprehensively studied. Shubnikov–de–Haas oscillations analysis yielded the effective mass of charge carriers, which proved to be very low, m* = 0.062×m0, and the value of fluctuations of hole density along the channel δp = 3.5×109 cm–2. The fractional Hall effect (filling numbers 8/3, 7/3, 5/3, 4/3) has been found for temperatures T < 5 K in strong magnetic fields. The studies of quantum interference effects related to weak localization and electron-electron interaction between charge carriers, firstly observed in such a high-mobility system, enabled the calculation of spin splitting Δ = 1.07 meV and the Fermi-liquid coupling constant Fσ0 = –0.12, which agree well with results obtained earlier [2].

 

● The influence of the shape of CrO2 nanoparticles, as well as the thickness and material properties of intergranular dielectric layers (chromium oxide Cr2O3 or chromium oxyhydroxide β-CrOOH) on tunnel resistance and magnetoresistance (MR) of pressed powder samples was studied. Non-metallic temperature resistance behavior and giant negative tunnel MR were found for all samples at low temperatures. The maximum value of MR at T ≈ 5 K and a relatively small magnetic field (H = 0.5 T) is approximately 37%. With increasing temperature, MR rapidly decreased (to ≈1% at H = 1 T, T ≈ 200 K) [3].

 

● The temperature dependences of resistance and magnetoresistance of two ceramics samples RuSr2(Eu1.5Ce0.5)Cu2O10−δ were analyzed after their long-term storage (10 years) in an ambient atmosphere and losing most of their superstoichiometric and some of their stoichiometric oxygen. The issues of stability of the superconducting state in ruthenocuprates, as well as the peculiarities of interaction of various types of hopping conductivity and superconductivity in granular magnetic materials, have been clarified [4].

 

● Studies of the negative magnetoresistance of multilayer carbon nanotubes in the temperature range of 4.2 ÷ 200 K and magnetic fields up to 9 T have shown that for small magnetic fields and low temperatures, the dependence of conductivity on the magnetic field is quadratic. Further, as the magnetic field increases, the dependence becomes logarithmic, which can be described by models of weak localization and interaction of charge carriers. It is shown that the quantum correction to the conductivity due to the weak localization of charge carriers significantly exceeds the addition due to the effect of the charge carriers’ interaction. Within the framework of these models, using experimental data on the field and temperature dependence of magnetoresistance, the Fermi energy, the value of the charge carrier interaction constant, and the exact form of the temperature dependence of the phase relaxation time for the wave function of the charge carriers were estimated [5].

 

● Using the example of a pressed sample made of chromium dioxide nanoparticles covered with insulating shells, the connection between the electron transport subsystem and the magnetic subsystem in granular spin-polarized metals was studied. It is shown that the spin-polarized tunnel transport current can affect the characteristic fields of the coercive force for the percolation cluster, which is formed in the sample with decreasing temperature [6].